For anyone having trouble locating the php.ini file, mine was located at /etc/php/7.0/fpm/php.ini. Placing a php.ini file in the /wp-admin folder did not work for me. I also ended up rebooting the server after I made changes to php.ini, then the new upload limit worked perfectly.
One thing that got me initially when the suggested changes didn't work, was that in addition to restarting nginx, I also had to restart php-fpm as well before I was able to successfully upload files to Wordpress.
"# service php-fpm restart"